REST API guidelines encourage that endpoints should enforce strict
handling of parameters to allow extension in the future.

If an endpoint supports no parameters, it should return an error
to allow adding them at a later point.

- added a ensure_no_params to add endpoints
- added tests for each each endpoint for "no-params"
- fixed crash if HttpRequest::get_...() tries to create a std::string
  from a nullptr

RB: 22172